Several metabolic pathways present in Streptococcus mutans have been examined using mutant analysis techniques. Two enzyme systems for ammonia assimilation have been identified: glutamate dehydrogenase and the coupled reactions of glutamine synthetase and glutamate synthase. The primary pathway for sucrose utilization has also been determined. Catabolism of sucrose is initiated by an inducible phosphoenolpyruvate-dependent sucrose phosphotransferase system followed by an intracellular sucrose 6-phosphate hydrolase.